Impeller

ABSTRACT

An axial flow rotary blood pump including an impeller ( 5 ) adapted to be magnetically rotated within a housing by the interaction of magnets disposed on or in the impeller and stators disposed on or in the housing. The impeller includes at least one support ring ( 2 ) supporting a plurality of blades ( 4 ), and a hydrodynamic bearing ( 3 ) that operates at least axially and radially in respect of an axis of rotation of the impeller ( 5 ).

FIELD OF THE INVENTION

The present invention relates to improvements in implantable axial flowrotary blood pumps.

BACKGROUND OF THE INVENTION

Cardiovascular disease remains a leading cause of death in the developedworld, responsible for more than 40% of deaths in Australia and in theUnited States. Annual diagnoses of new cases of heart failure in theUnited States have reached 550,000, leading to a population ofapproximately 4.7 million people afflicted by the disease; annual costestimates for heart failure treatment range from USD$10 billion to $38billion. Cardiac transplantation provides substantial benefit forpatients with severe heart failure, however there is a gross disparitybetween the numbers of potential recipients (800,000 p.a. worldwide) andsuitable transplant donors, approximately 3,000 p.a. worldwide.Consequently, there is a clear need for development of an effectiveheart support device.

In the past, Ventricular Assist Devices (‘VADs’) or Left VentricleAssist Devices (‘LVADs’) have been developed to provide support to theheart and are typically used for temporary (bridge-to-transplant andbridge-to-recovery) and permanent (alternative-to-transplant) support ofpatients. Generally, support for the left ventricle with an assistdevice (rather than a total artificial heart) is sufficient to restorecardiovascular function to normal levels for patients with terminalcongestive heart failure. As a consequence of the shortage oftransplants, there is a focus on long term alternative-to-transplantsupport in device development. The initial VADs developed were pulsatile(implanted and external to the body) and these have demonstratedenhanced survival and quality of life for patients with end-stage heartfailure compared with maximal medical therapy. However these devices aregenerally large, cumbersome, inefficient, prone to mechanical failureand costly.

It has been noted that continuous flow rotary VADs are generallysimpler, smaller and more reliable, as well as cheaper to produce, thanthe earlier pulsatile systems. For this reason, continuous flowcentrifugal devices, such as the VentrAssist™ LVAD, have emerged as thedefinitive forms of technology in the field of cardiac assistance.

A prior art implantable axial flow rotary blood pump is described inU.S. Pat. No. 5,370,509—Golding et al. This pump includes two blade setsand a support ring. The primary blade set functions as a thrust bearingto pump the blood directly from the inlet to the outlet. The secondaryblade set functions to divert blood around the outer surface of theimpeller. This diversion of blood is forced through a radially extendingrestriction. The effect of which is to create a fluid bearing thatsuspends the impeller only in the axial direction. The pump disclosedwithin this document has two main disadvantages.

The first disadvantage is that the blood paths disclosed in thatdocument are not perfected. The subsidiary blood flow around theimpeller is pushed in the same direction as the primary blood flowthrough the middle of the impeller. This type of blood path requiresrelatively high energy to maintain and generally lacks efficiency.

The second disadvantage is that secondary blade set may inducethrombogenesis and/or haemolysis within the pump due their shape.

Another prior art pump is disclosed in U.S. Pat. No. 6,227,797—Wattersonet al. It is a centrifugal rotary blood pump with a hydrodynamicallysuspended impeller. The main disadvantage with this device is that theimpeller of this pump includes complex blade geometry which increasesthe cost of manufacturing.

U.S. Pat. No. 5,211,546—Isaacson et al., discloses an axial flow rotaryblood pump wherein the impeller is only hydrodynamically suspended inthe radial direction relative to the axis of rotation. Additionally, thepump disclosed therein includes a hub or spider to position theimpeller. Hubs and spiders typically generate a location within the pumpof blood flow stagnation. Locations or points of stagnation within thechannel of blood flow should not be avoided to reduce the chance orlikelihood of thrombogenesis or blood clots.

U.S. Pat. No. 6,100,618—Schoeb et al. describes an axial flow pump witha simplifier motor rotor design. This pump is not suitable as animplantable blood pump design and the impeller within the pump is onlyradially hydrodynamically suspended.

It is an object of the present invention to address or ameliorate one ormore of the abovedescribed problems of the prior art.

BRIEF DESCRIPTION OF THE INVENTION

In a first aspect the present invention consists in an axial flow rotaryblood pump including an impeller adapted to be magnetically rotatedwithin a housing by the interaction of magnets disposed on or in theimpeller and stators disposed on or in the housing, characterised inthat said impeller includes at least one support ring supporting aplurality of blades, and a hydrodynamic bearing that operates at leastaxially and radially in respect of an axis of rotation of the impeller.

Preferably said hydrodynamic bearing exclusively suspends said impellerwithin a cavity.

Preferably said hydrodynamic bearing is formed by angular pads.

Preferably said support ring includes the hydrodynamic bearing.

Preferably said support ring includes the magnets.

Preferably said plurality of blades extend from the support ring towardsthe centre of the pump.

Preferably said the blades have a decreasing pitch to straighten bloodflowing out of the pump.

Preferably said pump is spider-less and sealless.

Preferably said impeller, when in use, experiences retrograde blood flowaround its periphery.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described withreference to the accompanying drawings wherein:

FIG. 1 is a perspective and cross-sectional view of a first preferredembodiment of the present invention;

FIG. 2 is a top view of the first embodiment shown in FIG. 1;

FIG. 3 is a cross sectional view of the first embodiment;

FIG. 4 is a perspective view of a second embodiment;

FIG. 5 is a side view of the second embodiment shown in FIG. 4;

FIG. 6 is a cross-sectional view of the second embodiment;

FIG. 7 shows an exploded perspective view of the second embodiment; and

FIG. 8 shows an enlarged and rotated view of a portion of the secondembodiment.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pump assemblies according to various preferred embodiments to bedescribed below, all have particular, although not exclusive,application for implantation within a patient. In particular, these pumpassemblies may be used to reduce the pumping load on a patient's heartto which the pumping assembly is connected. There may be otherapplications suitable for use with embodiments of the present inventionand these may include use as: perfusion pumps, applications requiringthe pumping of fragile fluids, external short term surgical blood pumps,and/or long term implantable blood pumps.

In practice, the preferred embodiments of the present invention may beperformed by placing the blood pump entirely within the patient's bodyand connecting the pump between the apex of the left ventricle of thepatient's heart and the ascending aorta so as to assist left side heartfunction. It may also be connected to other regions of the patient'scirculation system including: the right side of the heart and/or distalregions of a patient such as the femoral arteries or limbs.

In a first preferred embodiment depicted in FIGS. 1, 2 & 3, the bloodpump 15 includes an impeller 5 which is fully sealed within the pumpbody or housing 23. The impeller 5 has five spaced apart blades 4,extending from a central shaft 1, and connected to a support ring 2.

Preferably the impeller 5 is urged to rotate, in use, by an electricmotor. In a preferred embodiment, the electric motor may include severalsets of electrical coils or stators 17 mounted on or about the housing23 and a plurality of permanent magnets 7 embedded or encased within theblades 4 of the impeller 5. When in operation, the electric coilssequentially energise and exert an electromagnetic force on the impeller5 and the permanent magnets 7. If the pump is properly configured, thesequential energising of the electric coils or stators 17 will cause theimpeller 5 to rotate. The electric coils or stators 17 may be mounted inan axial and/or radial orientation, in relation to the axis of rotationof the impeller.

When the impeller 5 is rotated, the blades 4 push a fluid, for exampleblood, in an axial direction relative to the axis of rotation of theimpeller 5 and generally towards an outlet 21. The support ring 2 has agenerally rectangular cross section excluding the portions which formthe hydrodynamic bearings 3. The generally rectangular cross sectionallows square or rectangular cross-section permanent magnets 7 to beeasily inserted within the support ring 2. The benefit is that it iseasier to manufacture magnets in a square or rectangular cross-sectionshape than more complex shapes as provided by in the prior art. Thesupport ring 2 may also be of hollow construction to minimise weightand/or to reduce complexity of construction.

The impeller 5 includes four hydrodynamic bearings 3. The surface ofhydrodynamic bearings 3 is generally angled between 0° and 90° relativeto the axis of rotation so as to cooperate with an inner surface of thehousing 23 to generate a hydrodynamic force away from the inner surfaceof the cavity 14. The combined effect of these hydrodynamic bearings 3is to hydrodynamically suspend the impeller 5 within the housing 23,when in use. The most preferred angle for the hydrodynamic bearings 3 isapproximately 45°. These hydrodynamic bearings 3 produce axial andradial component vectors. Preferably, the hydrodynamic bearings 3 supplyat least an axial component vector to suspend the impeller 5 in an axialdirection, which is generally parallel to the axis of rotation of theimpeller 5.

Four spaced apart permanent magnets 7 are embedded within the supportring 2 of the impeller 5. Whilst the permanent magnets 7 may be placedin any location within the support ring 2, the most optimal positionsfor the permanent magnets 7 are shown in FIG. 2. It may be important tobalance the positions of the magnets to increase impeller stability andbalance.

The hydrodynamic bearings 3 are mounted on the upper surface and thelower surface of the support ring 2. These hydrodynamic bearings 3provide a zero net thrust force which is capable of hydrodynamicallysuspending the impeller 5 in the pump housing 23, when in use. Thehydrodynamic bearings 3 may also be used in conjunction with otherbearings means such as magnetic bearings.

The blood pump 15 includes an inlet 22 and an outlet 21 formed inhousing 23. Between the inlet 22 and the outlet 21 is pumping cavity 14,which allows fluid communication throughout the pump, when in use.Impeller 5 rotates within cavity 14 and its blades 4 supply pumpingmotion to the blood, to be pumped when in use.

The housing 23 includes machined surface on the wall of the cavity 14.This machined surface may include an upper inner surface 12, middleinner surface 13 and a lower inner surface 26. The upper inner surface12, middle inner surface 13 and/or the lower inner surface 26 cooperatewith at least a portion of outer surfaces of the impeller 5 to form, ineffect, hydrodynamic bearings 3. In particular, these portions of thesurfaces include the outer surface of the support ring 2 and/or thehydrodynamic bearings 3 mounted on the support ring 2.

When impeller 5 is rotated, the hydrodynamic bearings 3 may preferablycooperate with a proximate portion of the angular inner surfaces 12 & 26of the cavity 14. Thereby, when blood passes through a gap 20 locatedbetween the hydrodynamic bearing 3 and inner surface 26 of the cavity14, the impeller 5 experiences a hydrodynamic thrust force. This thrustforce acts upon the impeller 5 in a direction away from the inner wallsof the housing 23. The net force of all of the hydrodynamic bearings 3may result in the impeller 5 being partially or exclusivelyhydrodynamically suspended within the cavity 14.

The blood pump 15 of the first embodiment is in an axial flowconfiguration. The impeller 5, in use, is magnetically urged to rotateby the electro-magnetic interaction between permanent magnets 7 embeddedor encased within the support ring 2 and the electromagnetic coilsforming stators 17 mounted in a radial orientation in respect the axisof rotation of the impeller 5. Preferably, there are three electriccoils forming stators 17, however the number of coils may be amendedwithout generally affecting the functionality of this embodiment, solong as there are at least two coils. It should be noted that other coilconfigurations may also be used and these configurations may includeaxial mounting configurations.

The hydrodynamic bearings 3 have a generally wedge shaped side profileso as to generate a hydrodynamic force when rotated within thecomplementary shaped cavity 14. Please note that the number and size ofthe hydrodynamic bearings 3 may be also amended without departing fromthe scope of the present invention. Other configurations of hydrodynamicbearings 3 may include one hydrodynamic bearing mounted on each side ofthe impeller 15 and the bearing may run along the entire length of thesupport ring 2.

The hydrodynamic bearings 3 may be constructed to balance thehydrodynamic thrust forces and to suspend the impeller 5 away from theinner surfaces of the cavity 14.

The impeller 5 includes at least an axial and a radial component to thehydrodynamic thrust force generated by the angular surface of thehydrodynamic bearings 3. The hydrodynamic force imparted, in thepreferred embodiment, acts simultaneously in both an axial and radialdirection with respect to the orientation of the impeller 5.

It is important to note that in order to function safely and reliably,when in use, preferred embodiments of the present invention will includefeatures that limit thrombogenesis and haemolysis and which add to themechanical reliability of the pump. Preferably, the impeller of thepreferred embodiments may include at least some amount of dimensionalstability to prevent the blades and/or impeller changing their shape orconfiguration, in situ. Small dimensional changes in the shape orconfiguration of impeller 5 or housing 23 may occur due to warping ortwisting through regularly use of the pump. Dimensional stability isgenerally increased or improved by the inclusion of support structuresparticularly in regard to the impeller 5. These support structures mayinclude the support ring 2.

The impeller 5 may also include increased dimensional stability, whichis supplied by the generally square or rectangular cross-section of thesupport ring 2. The support ring 2 is joined to the blades 4 in thisconfiguration to prevent or limit the amount or severity of twisting,warping and/or other undesirable dimensional deformation.

The shaft 1 is preferably centered within the periphery of the impeller5 and is orientated in an axial direction. The blades 4 of this firstembodiment are generally thin and arcuate in shape and may incorporatefeatures to minimise drag and/or shear forces.

The first embodiment preferably operates at speeds of between 1500 rpmto 4000 rpm. The preferred outer blade diameter is 40 mm, outer housingaverage diameter is 60 mm and the housing axial length is 44 mm.

In FIGS. 4, 5, 6, 7 & 8, a second embodiment of the present invention isshown. An impeller 104 is provided for by the embodiment and includes acentral shaft 103 and a support ring 114. Extending from the internal orinterior surface of the support ring 114 towards the centre of the pump110 are a plurality or set of blades 105. In this preferred embodiment,three blades comprise the said blade set 105. However any number ofindividual blades may be used to construct the blade set 105.

The blades 105 fully extends from the support ring 114 to abut againstthe central shaft 103.

The support ring 114 preferably includes: two sets of permanent magnets102 & 115; hydrodynamic bearing surfaces 101 and channels 106 formedbetween the hydrodynamic bearing surfaces 101.

The upper set of permanent magnets 102 extend from the base of thechannels 106 in the upper surface into the support ring 114. In thisembodiment, the upper set of permanent magnets 102 comprise fourpermanent magnets aligned as to have the northern pole of the magnetsfacing up. Preferably, the upper set of permanent magnets 102 extendsalmost throughout the entire width of the support ring 114 withoutinterfering with the hydrodynamic bearing surface 101 on the lower sideof the support ring 114. The lower set of permanent magnets 115 works inan inverse manner to the upper set of permanent magnets 102. Thenorthern pole of the lower set of permanent magnets 115 faces downwards.The permanent magnets are disposed alternately in respect of polarityand are spaced at 45° intervals. The permanent magnets 102 & 115 arejacketed beneath a thin layer of impermeable biocompatible material toprevent corrosion or bio-toxic leaking.

This embodiment includes an impeller 104, which is designed to berotated clockwise, with four hydrodynamic bearing surfaces 101. Thehydrodynamic bearing surface 101 forms a pad which covers the upper faceof the support ring 114 and extends downwardly and at an anti-clockwiseangle to the lower face of the support ring 114. The angular extension107 of the hydrodynamic bearing surface 101 may generate a hydrodynamicbearing that is capable of acting at least axially and/or radially inrespect of the axis of rotation of the impeller 104. The hydrodynamicbearing may also act in respect of other degrees of freedom.

Each hydrodynamic bearing surface 101 includes a leading edge and atrailing edge. The leading edge is the edge that leads the trailing edgewhen the impeller is rotated in a clockwise direction. Preferably, theleading edge is 50 μm lower than the trailing edge. The angularlysurface cooperates with the interior of the pump housing to form arestriction. This restriction generates a thrust force perpendicular tothe bearing surface. When the impeller 104 is in use, the hydrodynamicbearings suspend the impeller 104 within the pump housing 120. Thehydrodynamic bearing surfaces 101 have a generally wedge shapedappearance.

The channels 106 are approximately 0.5 mm deeper than the leading edgeof the hydrodynamic bearing. This channel 106 may allow retrograde bloodflow over the surface of the impeller 104, when in use. This isdescribed in greater detail further on in this specification.

The pump 110 pumps blood from the inlet 108 to the outlet 109 by therotation of impeller 104, which in turn rotates a plurality of blades105. The impeller is mounted within an upper 120 and lower housing 119.The housings 120 & 119 are preferably joined by laser welding atlocation 117. When in use, the impeller 104 is urged to rotatemagnetically through the synchronised activation of the stators 112cooperating with the permanent magnets 102. The preferred speed ofrotation of impeller 104 is approximately 2,000 rpm. However, it will beappreciated that small changes in shape and diameter of impeller 104will greatly effect the preferred speed of rotation.

Preferably, the internal portions of the pump 110 are encapsulatedwithin a casing shell 111 and two end caps 126. The end caps 126 andcasing shell 111 may be constructed of a biocompatible Titanium alloywhich may be joined and sealed by laser welding. It includes a casingshell hole 127 to allow access to the interior of the pump by electronicleads for pump control, power and data.

Each blade 105 forms a screw thread configuration around the centralshaft 103. The pitch of the screw thread of the individual bladesdecreases as the blade extends away form the inlet of the pump 110. Thisallows some the torsional force applied to the blood being pumped to betranslated into thrust in the direction of the outlet and straightensthe flow of blood leaving the pump. Preferably, using this type ofconfiguration may reduce or eliminate the need for flow straighteners inthe outflow of the pump 110.

The retrograde blood flow in the pump 110, has an elevated pressure inoutlet 109 when compared to the pressure level in the inlet 108 as aresult of the rotation of impeller 104. The pressure differentialcreated between the outlet 109 and inlet 104 means that blood will,where possible, attempt to flow back to the inlet 104. The blood ispurposively given an opportunity to do this by the gap 113 which occursbetween the outermost surface of the impeller 104 and the innermostsurface of the housings 119 & 120, which forms a cavity 116 for theimpeller 104 to rotate within. The gap 113 is the location where ahydrodynamic bearing is created by the interaction of the hydrodynamicbearing surfaces 101 and the walls of the cavity 116. Preferably the gap113 is approximately 80 μm. The gap 113 is preferably small enough so asexclude a majority of blood cells from this area by fluid forces. Thisexclusion of red blood cells reduces haemolysis caused by the bearingforces. Additionally, the constant flow of fresh blood across theoutermost surfaces of the impeller 104 reduces the chance or likelihoodof thrombogenesis in the vicinity of the impeller 104.

The stators 112 are in an axial configuration around the impeller 104and are formed from twelve independent coils mounted directly onto aprinted circuit board 118. When the pump 110 is assembled, the coils areinserted within twelve wells 125 formed in the outer surface of thehousing 120. The printed circuit board 118 forms part of the controlsystem for the pump 110 and is backed by an iron metal yoke to improveEMF efficiency.

In FIG. 8, the twelve stator coils are shown at one instance in timewhen the coils are firing to urge the impeller 104. The twelve statorcoils are depicted in three groups 121, 122 & 123. The three groups ofcoils 121, 122, & 123 cooperate with the permanent magnets 102 & 115 ofthe impeller 104 to rotate it. In the instance shown, the first group ofcoils 121 have their north poles distal from the printed circuit board118. The second group of coils 123 have an inverted polarity and thethird polarity is not charged. The charging sequence of the groups ofcoils 121, 122, & 123 rotates clockwise and induces the rotation of theimpeller 104.

An advantage of both the abovementioned embodiments over the prior artis that the manufacture of impellers 5 and 104 is a separate machiningoperation to that of the respective support rings 2 and 114. As themagnets are carried by the support rings 2 and 114 and not the blades ofthe impeller 5 and 104 is of less complexity and therefore lessexpensive manufacture than that employed in prior art blood pumps withhydrodynamic bearings where the magnets are encapsulated within theblades.

The above descriptions only describe some of the embodiments of thepresent inventions and modifications. It may be obvious to those skilledin the art that further modifications can be made thereto withoutdeparting from the scope and spirit of the present invention.

1. An axial flow rotary blood pump including an impeller adapted to bemagnetically rotated within a housing by the interaction of magnetsdisposed on or in the impeller and stators disposed on or in thehousing, characterized in that said impeller includes at least onesupport ring supporting a plurality of blades, and a hydrodynamicbearing that operates at least axially and radially in respect of anaxis of rotation of the impeller.
 2. The axial flow rotary blood pump ofclaim 1 wherein said hydrodynamic bearing exclusively suspends saidimpeller within a cavity.
 3. The axial flow rotary blood pump of claim1, wherein said hydrodynamic bearing is formed by angular pads.
 4. Theaxial flow rotary blood pump of claim 1, wherein said support ringincludes the hydrodynamic bearing.
 5. The axial flow rotary blood pumpof claim 1, wherein said support ring includes the magnets.
 6. The axialflow rotary blood pump of claim 1, wherein said plurality of bladesextend from the support ring towards the centre of the housing.
 7. Theaxial flow rotary blood pump of claim 1, wherein said blades have adecreasing pitch to straighten blood flowing out of housing.
 8. Theaxial flow rotary blood pump of claim 1, wherein said housing isspider-less and seal-less.
 9. The axial flow rotary blood pump of claim1, wherein said impeller, when in use, experiences retrograde blood flowaround its periphery.
 10. (canceled)
 11. An axial flow row rotary bloodpump including: an impeller adapted to be magnetically rotated within ahousing by the interaction of magnets disposed on or in the impeller andstators disposed on or in the housing, wherein said impeller includes atleast one hydrodynamic thrust bearing and wherein said impeller includesat least one channel formed in the outer surface of the impeller topropel blood through the housing, when impeller is rotated within thehousing.
 12. An axial flow blood pump of claim 11, wherein at least onehydrodynamic thrust bearing is formed by the interaction of a portionthe outer surface of the impeller and a portion of the inner surface ofthe housing.
 13. An axial flow blood pump of claim 12, wherein one ofthe hydrodynamic thrust bearing generates a thrust force which includesan axial component relative to the axis of rotation.
 14. An axial flowblood pump of claim 12, wherein one of the hydrodynamic thrust bearinggenerates a thrust force which includes a radial component relative tothe axis of rotation.
 15. An axial flow blood pump of claim 12, whereinat least one hydrodynamic thrust bearing is formed by interaction of awedge shaped member disposed on the outer surface of the impeller.